Fortsättning på Internetprotokoll. Maria Kihl

Transkript

1 Fortsättning på Internetprotokoll Maria Kihl

2 Läsanvisningar Kihl & Andersson: 7.7, 7.9, intros i , 12.1, 12.4, 17.1, 18.1 (endast ping och traceroute) Stallings: 14.3 (ICMP), 24.2, 24.3, Forouzan 5th: 18.3, 19.2, 25.1, 26.1, 26.6, 31 2

3 Internetprotokollen 3

4 Datasäkerhet Det finns tre viktiga koncept vad det gäller datasäkerhet: 1. Skydd mot avlyssning (Privacy) 2. Skydd mot ändrad data (Integrity) 3. Autentisering (Authentication)

5 Skydd mot avlyssning (Privacy) Skydd mot avlyssning (eller privacy) betyder att meddelandet som sänds endast ska kunna förstås av mottagaren. För alla andra ska meddelandet vara oförståeligt. Privacy löses med kryptering av meddelandet.

6 Exempel på kryptering

7 Skydd mot ändrad data (Integrity) Skydd mot ändrad data (Integrity) betyder att meddelandet måste komma fram exakt så som det var sänt. Det får inte finnas några ändringar i meddelandet. Integrity kan tillhandahållas med message digests.

8 Message digest

9 Autentisering (Authentication) Autentisering (authentication) innebär att mottagaren måste vara säker på sändarens identitet. Autentisering av enheter kan lösas med lösenord eller så kallad challenge-response. Autentisering av meddelanden kan tillhandahållas med en digital signatur. En digital signatur är en message digest som är krypterad.

10 Challenge-response R b = Slumptal (Nonce)

11 Digital signatur

12 Internet security protokoll Följande tre säkerhetsprotokoll tillhandahåller privacy, integrity och authentication på olika protokollskikt: IPSec: Säkerhetsprotokoll för IPv4. SSL/TLS: Säkerhetsprotokoll för TCP. PGP: Säkerhetsprotokoll för (SMTP). Dessa protokoll kommer att gås igenom i fortsättningskursen Internetprotokoll.

13 Exempel: WWW World Wide Web (WWW) presenterades av Tim Berners-Lee 1989 vid CERN. Syftet med WWW var att möjliggöra för forskare att dela information på ett enkelt sätt. Det mer kommersiella WWW startades under tidigt 1990-talet med Netscape och Mosaic. Aftonbladet.se startades 1994 som den första stora nättidningen i Sverige. 13

14 Basic concept of WWW WWW is based on three basic parts: Web documents (pages) HyperTextMarkup Language (HTML) is used for static web documents Dynamic web documents are created with script languages (JSP, CGI, ASP, etc.) Universal Resource Locator (URL) Standardized way to identify the location of web documents HyperText Transfer Protocol (HTTP) Protocol for access of web documents on a web server 14

15 Universal Resource Locator (URL) A web document has four identifiers: Protocol, Host, Port and Path. An URL is defined as: protocol://host:port/path When standard HTTP port 80 is used it is omitted, for example: 15

16 HTTP HTTP is a text-based protocol with two basic types of messages: Requests and Responses. HTTP sets up and uses a TCP connection HTTP 1.1 uses persistent connections which means that all parts of the web document use the same TCP connection. 16

17 Basic operation of HTTP

18 Mapping from host name to IP address Application protocols use host names (for example However, TCP/IP uses IP addresses. The mapping from host name to IP addresses is performed by Domain Name System (DNS). 18

19 Basic operation of DNS 19

20 Domain Name space DNS uses a hierarchical name space and the whole Internet is divided into domains and subdomains. A domain name is a sequence of labels separated with dots, e.g. 20

21 Domain name space in DNS root 21

22 Example of labels and domains 22

23 Domain types The domain name space is divided into three different sections. 23

24 Domain Name Servers The domain name space is stored in special DNS servers. The servers are distributed and each domain or subdomain have their own servers. A host always knows the IP-address to its closest DNS server. 24

25 From name to address (1) angel1.heavennet.se angel2.angelnet.se 1. angel2.angelnet.se? ns.heavennet.se 25

26 From name to address (2) angel1.heavennet.se angel2.angelnet.se 2. angel2.angelnet.se? ns.heavennet.se 3. Ask ns.angelnet.se sunic.sunet.se 26

27 From name to address (3) angel1.heavennet.se angel2.angelnet.se 4. angel2.angelnet.se? ns.heavennet.se 5. IP = ns.angelnet.se 27

28 Internet Control Message Protocol (ICMP) The IP protocol has no error-reporting or errorcorrecting mechanism. The IP protocol also lacks a mechanism for host and management queries. The Internet Control Message Protocol (ICMP) has been designed to compensate for the above two deficiencies. It is a companion to the IP protocol.

29 ICMP in the TCP/IP stack

30 ICMP message Two types of messages: Error-reporting messages Query messages

31 Encapsulation The ICMP message is encapsulated in an IP datagram:

32 Error-reporting When an error in the IP datagram delivery is detected, ICMP reports the error to the source of the IP datagram. The error message includes the IP header and first 8 bytes of the original datagram.

33 Some Error reporting messages Destination unreachable: A router cannot route a datagram or a host cannot deliver a datagram. Source quench: A datagram is discarded due to congestion. Time exceeded: A datagram has been discarded since its TTL value has reached 0. Redirection: A host has the wrong default router, and needs to update its routing table.

34 Some ICMP Query messages Echo-request and Reply: Is used to determine if two systems (hosts or routers) have connection on the IP level. Timestamp request and reply: Is used to determine the round-trip time (RTT) between two systems. Router-Solicitation and Advertisment: Is used by a host to find the routers that are connected to its network.

35 Tentaexempel A B Switch C Router DNS Host A vill skicka en ICMP echo request till host C. Host A kan bara C:s symboliska namn c.citynetwork.se. Förutsätt att alla adress-cacher är tomma. 35

36 Debugging Tools There are several tools that can be used in the Internet for debugging. Some of them are: Ping Traceroute

37 Ping The Ping program uses ICMP echo-request and reply messages to find information about a destination.

38 Traceroute Traceroute (in UNIX) or Tracert (in Windows) can be used to trace the route of a packet from the source to the destination. It manipulates the TTL field in the IP header and uses two ICMP messages: Time Exceeded and Destination Unreachable to find the route of a packet.

39 Traceroute, example

40 Tentaexempel Förklara var i OSI-modellen följande protokoll hör hemma: HTTP, 802.3, TCP, PPP, IP,UDP, ICMP, ARP Dina svar ska vara motiverade! 40

41 Telenätet och mobila system Maria Kihl

42 Läsanvisningar Kihl & Andersson: 13, Stallings: 8.4, 10.1, 10.2, Forouzan 5th: 12.3, 14.1, 16.2 Läsanvisningarna definieras av innehållet på slides.

43 Det publika telenätet (PSTN) Copper cable Digital Local station Core network (SONET/SDH) Analog Access network

44 Data transfer in telephone networks The telephone core networks are digital. PCM in local stations Data transfer with 8-bits samples. The telephone networks use circuit switching. A connection is set up for each call. The core networks use Synchronous Time Division Multiplexing. 44

45 Hierarchical structure From the telephone to local station (end office), the analog data is transferred on the 0-4 khz frequency band. In the local station, PCM is used to create 8-bit samples that are coded and transmitted in the network using circuit switching and STDM. Also, there are gateways to the Internet and mobile networks.

46 Circuit switching

47 Control messages Switching stations (offices) communicate with standardized protocols using a separate network.

48 Comparison with the Internet In the Internet, control messages are sent the same path as data packets. Special protocols, for example ICMP, ARP, DNS Included in headers of data packets. In the telephone networks, the data transfer is separated from the control messages. Delays for setting up and tearing down connections. Very efficient data transfer with circuit switching.

49 Signaling System No. Seven (SS7) The protocol stack for telephone networks is called Signaling System No. Seven (SS7).

50 Reliability aspects A telephone switching station can be down only 6 minutes during 10 years. This means that: All software updates must be performed during runtime. All hardware parts are doubled for redundancy. Much automatic error detection and failure recovery mechanisms. 50

51 Internet access with xdsl xdsl (ADSL, VDSL, etc) is used for providing Internet access via the telephone access line.

52 Mobile cellular (telephone) networks Access network Base station Core network Mobile station

53 The Frequency is the main performance problem Very Low Frequency (VLF) KHz Low Frequency (LF) KHz (e.g. submarines) Medium Frequency (MF) MHz (e.g. radio stations) High Frequency (HF) 3-30 MHZ (e.g. radio stations) Very High Frequency (VHF) MHz (e.g. TV stations) Ultra High Frequency (UHF) GHz (e.g. mobile telephony) Super High Frequency (SHF) 3-30 GHz (e.g. WLAN and microwave links) Extremely High Frequency (EHF) GHz Optical transmission >300 GHz (e.g., IR, visible light, UV)

54 Together with mobility A cellular system should manage to maintain a connection even when the mobile station moves in high speeds, maybe across networks.

55 Cells and frequency reuse The network is geographically divided into cells. In each cell there is a base station. Each cell is given some frequencies. The frequencies are reused in other cells according to a specific pattern.

56 Cellular access network To core network BSC Base station controller Several cells are controlled by one base station controller.

57 Problems with mobility The necessary signal strength depends on the mobile station s distance to the base station (power control). The mobile stations can move to another cell (handover/handoff). The mobile station can move to another network, maybe in another country (roaming).

58 Multipel access Flera terminaler ska ha access till samma basstation. Protokoll för multipel access krävs. Cellulära nät använder Controlled access. Basstationen bestämmer vilken kanal en terminal får använda. Uplink och Downlink -kanaler kan använda olika metoder för kanaluppdelning. Det finns vanligtvis en gemensam kanal som alla terminaler lyssnar på.

59 Multipel access i mobila nät Olika kanaler används med olika MAC-protokoll för att Hitta en basstation Kontrollmeddelanden Dataöverföring Telefoni Etc. 59

60 Channelization (Multiple access) Three basic so called channelization techniques: Frequency-Division Multiple Access (FDMA) Time-Division Multiple Access (TDMA) Code-Division Multiple Access (CDMA)

61 Frequency-Division Multiple Access In FDMA, the terminals have separate frequency bands.

62 Time-Division Multiple Access In TDMA, the terminals use separate time slots on a shared frequency band.

63 Code-Division Multiple Access In CDMA, the terminals send data on the same channel at the same time but with different chip sequences.

64 2G/3G-system GSM (Global System for Mobile Communication) brukar kallas för 2G. UMTS (Universal Mobile Telecommunication System) brukar kallas för 3G. Gemensamt: Utvecklade främst för telesamtal. Använder liknande arkitektur för kärnnätet. Olika: Radioaccessen ger högre överföringshastigheter i UMTS.

65 Kärnnätet i GSM och UMTS Teletrafik PSTN Accessnät Kärnnät MSC CS-MGW UE RNC/BSC VLR HLR Basstation SGSN GGSN Datatrafik Internet

66 Förklaring till begreppen UE=User Equipment BSC = Base Station Controller RNC = Radio Network Controller MSC = Mobile Switching Centre CS-MGW = Circuit Switched Media Gateway SGSN = Serving GPRS support node GGSN = Gateway GPRS support node HLR = Home Location Register VLR = Visiting Location Register

67 Example: Finding a mobile station in GSM or UMTS The network is divided into Location areas, each controlled by one BSC. Also, there are administrative regions, each controlled by one MSC. The VLR contains information about all mobile stations in the region (location areas). The MSC pages the BSCs about the exact location of a mobile station,

68 GSM access GSM uses a combination of FDMA and TDMA. Originally developed only for voice data.

69 UMTS accessnät (UTRAN) UMTS Terrestrial Radio Network Använder frekvensmultiplex och CDMA. CDMA kräver power control, eftersom alla mobiler måste ha samma signaleffekt vid basstationen. Detta regleras 1500 ggr per sekund. Innhåller dynamisk allokering av kapacitet.

70 Dynamisk resursallokering i UMTS The capacity for each user is dynamically allocated (each 10 ms). This allows for a more efficient use of the frequency band.

71 Mobilt Internet Application centric Internet community TCP/IP de facto standards ATM, SDH, SS#7 Telecom operators Standard organizations Technology centric

72 Objective: More bandwidth and Internet access Today, mobile cellular networks are not only used for telephony. Internet applications require much more bandwidth! Circuit switching is not optimal for Internet applications. LTE is focused on higher data rates and Internet access.

73 Long Term Evolution (LTE) 4th generation mobile networks Difference compared to GSM/UMTS: Packet-switching! Main service is Internet access, not telephony! Higher data rates (of course) Solutions needed to provide Voice over LTE Higher data rates require much smaller cells than before, so called pico and femtocells.

74 Kärnnätet i LTE Accessnät HSS Kärnnät MME Internet UE enode B SGW PDN-GW

75 Förklaring till begreppen enode B: Evolved Node B MME = Mobility Management Entity SGW = Serving Gateway PDN GW = Packet Data Network gateway HSS = Home Subscriber Server Notera: Det går inte att ringa vanliga kretskopplade telesamtal med LTE:s arkitektur!

76 Circuit-switched fallback Circuit-switched fallback används i de svenska LTE-näten och innebär att telesamtal kopplas via GSM/UMTS-nätet. Kräver kommunikation mellan LTE och GSM/UMTS

77 Circuit-switched fallback Näten måste använda samma databas för användarna (HLR/HSS) PSTN Node B BSC MSC CS-MGW UE HSS enode B MME PDN GW Internet